Not many astronomical objects are also units of measurement. But one that is stands high in the east at nightfall, near the tip of one of the horns of Taurus, the bull.
You need a telescope to see the Crab Nebula because it’s not very bright at visible wavelengths. In X-rays, though, it’s one of the brightest objects in the sky. In fact, its X-ray brightness is defined as one crab — the basic unit for the brightness of all X-ray targets.
The nebula is the remnant of a supernova — a massive star that blasted itself to bits almost a millennium ago as seen from Earth. Shockwaves from the expanding debris heat gas and dust, causing them to emit X-rays. More X-rays come from electrons that are spiraling through the powerful magnetic field generated by the star’s dead core.
Studying the X-rays helps astronomers piece together the history of the star and the process of its destruction. They reveal the chemical composition of some of the star’s debris, which was produced in the star itself and during its demise. And they help trace the magnetic field that weaves through the nebula.
In fact, X-rays are important tools for studying many of the most powerful objects and events in the universe, which can reach temperatures of hundreds of millions of degrees. Hotter objects produce radiation at shorter wavelengths, with the hottest producing the shortest wavelengths of all, especially X-rays.
More about X-ray astronomy tomorrow.
Script by Damond Benningfield